This makes it so test-cors.html is a real file in doc/source so it's easy for
those in the know to jump in there with a `python -m SimpleHTTPServer` and
point their webbrowser to `http://localhost:8000/test-cors.html`.
The example html and javascript still appear in the docs in their entirety
using the Sphinx literal include directive.
Change-Id: Ia0ba36df6c58795e3764fa53b7f585dcc1b3be07
